Methods and apparatus for discovering a powerability condition of a computer network

ABSTRACT

The invention is directed to techniques for discovering a powerability condition of a computer network such as the existence of a remotely powerable device attached to a connecting medium of the computer network. Such detection can then control whether a remote power source (e.g., a data communications device such as a switch) provides remote power (e.g., phantom power) to the computer network. One arrangement of the invention is directed to an apparatus for discovering a powerability condition of a computer network. The apparatus includes a signal generator, a detector and a controller which is coupled to the signal generator and the detector. The controller configures the signal generator to provide a test signal to a connecting medium of the computer network, and configures the detector to measure a response signal from the connecting medium of the computer network. The controller then indicates whether a remotely powerable device connects to the connecting medium of the computer network based on the response signal. Accordingly, if the apparatus discovers a remotely powerable device attached to the computer network (i.e., the power requirement condition of the network), the apparatus can provide power to the device remotely (e.g., through the connecting medium). However, if the apparatus does not discover a remotely powerable device attached to the computer network (e.g., another power requirement condition), the apparatus can avoid providing power remotely and thus avoid possibly damaging any non-remotely powerable device on the computer network.

BACKGROUND OF THE INVENTION

[0001] There is a wide variety of data communications networks suitablefor carrying data between devices. For example, Ethernet is a widelyused architecture for local-area networks (LANs). The architecture forsuch a computer network, along with variants defined in the IEEE 802.3standard, is the result of work performed at a variety of companies.

[0002] Initially, the purpose of an 802.3 network was to carry datacommunications exclusively. All of the devices attached to such acomputer network included their own power supplies and derived powerfrom these power supplies. Accordingly, each device operated as astandalone system with unlimited local power.

[0003] Today, there exists a wide range of devices for which remotepowerability is highly desirable. For example, it would be convenient ifcertain devices, which can attach to an 802.3 network, could draw powerfrom the 802.3 network in order to operate properly. Examples of suchdevices include Internet telephones (IP phones) andsecurity/surveillance devices.

SUMMARY OF THE INVENTION

[0004] Unfortunately, if a power source (e.g., a power supply) simplyapplies power to an 802.3 computer network in order to power a remotelypowerable device on that network, there is a high risk of damaging anynon-remotely powerable device on the network, i.e., a device which doesnot require and draw remote power. A conventional non-remotely powerabledevice typically includes circuitry (e.g., a network terminationcircuit) that is unable to handle power provided over a computernetwork. In the event of remote power application, such circuitry canoverheat or burn out resulting in permanent damage to the non-remotelypowerable device.

[0005] Furthermore, applying power to a computer network that does notrequire such power runs the risk of creating adverse conditions withinthe computer network itself. For example, applying power to an 802.3network runs the risk of generating broadcast firestorms within the802.3 network.

[0006] In contrast, the invention is directed to techniques fordiscovering a powerability condition of a computer network such as theexistence of a remotely powerable device attached to a connecting mediumof the computer network. Such detection can then control whether aremote power source (e.g., a data communications device such as aswitch, or a mid-span device such as a patch panel) provides remotepower to the computer network (e.g., phantom power from a VDC powersource connected to digital communication lines of the network, directpower, etc.).

[0007] One arrangement of the invention is directed to an apparatus fordiscovering a powerability condition of a computer network. Theapparatus includes a signal generator, a detector, and a controllerwhich is coupled to the signal generator and the detector. Thecontroller configures the signal generator to provide a test signal to aconnecting medium of the computer network, and configures the detectorto measure a response signal from the connecting medium of the computernetwork. The controller then indicates whether a remotely powerabledevice connects to the connecting medium of the computer network basedon the response signal. Accordingly, if the apparatus discovers aremotely powerable device attached to the computer network (i.e., apowerability condition of the network), the apparatus can provide powerto the device remotely (e.g., through the connecting medium). However,if the apparatus does not discover a remotely powerable device attachedto the computer network (e.g., another powerability condition of thenetwork), the apparatus can avoid providing power remotely and thusavoid possibly damaging any non-remotely powerable devices on thecomputer network.

[0008] In one arrangement, the computer network supports connection of aremotely powerable device that receives, during normal operation, anoperating voltage having a first voltage magnitude. Here, the controllerconfigures the signal generator to supply, as the test signal, a testvoltage having a second voltage magnitude that is substantially lessthan the first voltage magnitude. Accordingly, if there is no remotelypowerable device connecting to the computer network but there is anon-remotely powerable device that connects to the computer network, thecurrent resulting from the application of the second (lower magnitude)test voltage is less likely to cause damage to the non-remotelypowerable device compared to the current that would result from theapplication of the first (higher magnitude) test voltage.

[0009] In one arrangement, the controller configures the signalgenerator to supply, to the connecting medium, (i) a first voltageduring a first time period, and (ii) a second voltage that issubstantially different than the first voltage during a second timeperiod. Preferably, the controller configures the signal generator toapply one of a positive and negative test voltage to the connectingmedium as the first voltage (e.g., −5 volts), and the other of thepositive and negative test voltage to the connecting medium as thesecond voltage (e.g., +5 volts). This arrangement enables the controllerto determine whether a remote device, which allows current to flow whenin only one-direction (e.g., a remotely powerable device), connects tothe computer network and, if so, whether that device is properlyconnected (or reverse-wired).

[0010] In one arrangement, the connecting medium includes (i) a firstconnecting link having a local end that terminates at a firsttransformer and a remote end, and (ii) a second connecting link having alocal end that terminates at a second transformer and a remote end. Inthis arrangement, the controller preferably configures the signalgenerator to apply the test signal to the connecting medium through acentertap of the first transformer and a centertap of the secondtransformer. This arrangement is particularly advantageous in 802.3networks since such networks typically use centertapped transformersthus enabling the invention to utilize existing network-relatedcomponents.

[0011] In one arrangement, the connecting medium includes a local endand a remote end. Preferably, the controller selectively identifies,through the local end of the connecting medium, one of (i) a backwardswired device condition at the remote end, (ii) an open condition at theremote end, (iii) a remotely powerable device condition at the remoteend, and (iv) a shorted/non-powerable device condition at the remoteend. Accordingly, the controller can distinguish between a variety ofcomputer network conditions (i.e., powerability conditions).

[0012] One arrangement of the invention is directed to a datacommunications device (e.g., a switch, a hub, a router, a bridge, etc.)or other device (e.g., a patch panel) that includes normal operatingcircuitry which communicates with a remote device over a computernetwork during normal operation, and power circuitry coupled to thenormal operating circuitry. In this arrangement, the power circuitry,which is capable of discovering whether the remote device is remotelypowerable over the computer network, is built into the datacommunications device itself.

[0013] Another arrangement of the invention is directed to a remotelypowerable device having normal operating circuitry which couples to aconnecting medium of a computer network, and a powerability indicatorwhich couples to the normal operating circuitry. The powerabilityindicator is capable of receiving a test signal from the connectingmedium of the computer network, and providing a response signal to theconnecting medium of the computer network to enable discovery of theremotely powerable device based on the response signal.

[0014] Another arrangement of the invention is directed to a computerprogram product that includes a computer readable medium havinginstructions stored thereon for discovering a powerability condition ofa computer network. The instructions, when carried out by a processor,cause the processor to perform the steps of: (i) providing a test signalto a connecting medium of the computer network; (ii) measuring aresponse signal from the connecting medium of the computer network; and(iii) determining whether a remotely powerable device connects to theconnecting medium of the computer network based on the response signal.

[0015] The features of the invention, as described above, may beemployed in data communications devices and other computerized devicessuch as those manufactured by Cisco Systems, Inc. of San Jose, Calif.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

[0017]FIG. 1 is a block diagram showing a remote powerability systemwhich is suitable for use by the invention.

[0018]FIG. 2 is a flow diagram illustrating a procedure performed by apower apparatus of FIG. 1.

[0019]FIG. 3 is a block diagram showing an arrangement of componentswhich is suitable for use for forming a portion of the remotepowerability system of FIG. 1.

[0020]FIG. 4 is a flow diagram illustrating a procedure which issuitable for use as a step of providing a test signal and measuring aresponse signal of FIG. 2.

[0021]FIG. 5 is a circuit diagram showing certain circuit elementdetails which are suitable for use in particular components of FIG. 3.

[0022]FIG. 6A is a block diagram showing a component arrangement havingan open condition for comparison to the arrangement of FIG. 3.

[0023]FIG. 6B is a block diagram showing a component arrangement havinga backwards wired device condition for comparison to the arrangement ofFIG. 3.

[0024]FIG. 6C is a block diagram showing a component arrangement havinga shorted/non-powerable device condition for comparison to thearrangement of FIG. 3.

[0025]FIG. 7 is a block diagram showing a network configuration whichincludes the remote powerability system of FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0026] A remotely powerable device is a device which requires and drawspower from a remote power source for normal operation. The invention isdirected to techniques for discovering a powerability condition of acomputer network such as the existence of a remotely powerable deviceattached to a connecting medium of the network. Such detection can thencontrol whether a remote power source (e.g., a data communicationsdevice such as a switch) provides remote power (e.g., phantom power ordirect power) to the network. That is, if it is determined that aremotely powerable device is attached to the network, the remote powersource can provide power to the device remotely (e.g., through theconnecting medium). However, if no remotely powerable device isdiscovered, the remote power source can avoid providing power remotely,and thus avoid possibly damaging any non-remotely powerable devices onthe network. Such techniques may be employed in data communicationsdevices and other computerized devices such as those manufactured byCisco Systems, Inc. of San Jose, Calif.

[0027]FIG. 1 shows a remote powerability system 20 which is suitable foruse by the invention. The system 20 is a computer network which includesa device 22-A (e.g., an IP phone) and a device 22-B (e.g., an IPswitch). The devices 22-A, 22-B (collectively, devices 22) communicatewith each other through a connecting medium 24. In one arrangement, thedevices 22 include physical layer devices (PHY), and the connectingmedium 24 includes a Medium Dependent Interface (MDI) having multiplelines for carrying signals between the devices 22 (e.g., 10BaseT,100BaseT, etc.). The system 20 further includes a power apparatus 26which connects with the device 22-B through connections 28. The powerapparatus 26 includes a controller 30, a signal generator 32 and adetector 34. Further details of the invention will now be discussed withreference to FIG. 2.

[0028]FIG. 2 shows a procedure 40 which is performed by the powerapparatus 26 in order to discover a powerability condition of the system20 of FIG. 1. In particular, the power apparatus 26 performs theprocedure 40 to determine whether the device 22-A is remotely powerable.

[0029] In step 42, the apparatus 26 provides a test signal (e.g.,multiple voltages) to the connecting medium 24, and measures a responsesignal (e.g., current in response to the multiple voltages). Inparticular, the controller 30 configures the signal generator 32 toprovide the test signal to the connecting medium 24 of the system 20through the device 22-B. Additionally, the controller 30 configures thedetector 34 to measure the response signal from the connecting medium 24through the device 22-B.

[0030] In step 44, the apparatus 26 indicates whether a remotelypowerable device connects to the connecting medium 24 based on theresponse signal. In particular, the controller 30 stores an indicationsignal result of the detector 34 which is based on the response signal.The indication signal result indicates whether the device 22-A is aremotely powerable device.

[0031] In step 46, the apparatus 26 proceeds to step 48 if it discoversthat a remotely powerable device connects to the connecting medium 24.Otherwise (i.e., if the apparatus 26 does not discover a remotelypowerable device connecting to the connecting medium 24), the apparatus26 proceeds to step 50.

[0032] In step 48, when the apparatus 26 has discovered that the device22-A is remotely powerable, the apparatus 26 provides power to thedevice 22-A. As will be explained in further detail later, the apparatus26 preferably provides phantom power to the device 22-A through theconnecting medium 24. The apparatus 26 then terminates the procedure 40.

[0033] In step 50, when the apparatus 26 has not discovered a remotelypowerable device connecting to the system 20, the apparatus 26determines whether it should continue operation. If not, the apparatus26 terminates the procedure 40 (e.g., in response to a shutdown or resetcommand). If the apparatus 26 determines that it should continueoperation, the apparatus 26 proceeds to step 52.

[0034] In step 52, the apparatus 26 allows a delay time period toelapse, and then proceeds back to step 42 to repeat the procedure 40. Inone arrangement, the apparatus 26 waits a relatively short period oftime (e.g., one to two minutes) before proceeding back to step 42.

[0035]FIG. 3 is a block diagram showing, by way of example only, anarrangement 60 of components which is suitable for use for the remotepowerability system 20 of FIG. 1. Each device 22 includes normaloperating circuitry 62 and a set of transformers 64, 66. Eachtransformer 64, 66 includes a centertap 68 that divides a portion of thetransformer 64,66 into an upper coil and a lower coil, and providesdirect access to the connecting medium 24.

[0036] The invention relies on distinguishing connection attributesbetween (i) a remotely powerable device at a remote end of a networkconnection, (ii) a reverse-wired remotely powerable device at a remoteend of a network connection, (iii) an open condition at a remote end ofa network connection, and (iv) a non-remotely powerable device at aremote end of a network connection or a short in the network connection.In one arrangement, the remotely powerable device allows current to flowin only one direction through the network connection, the reverse-wiredremotely powerable device allows current to flow only in the oppositedirection, the open condition prevents current from flowing in eitherdirection, and the non-remotely powerable device/shorted-conditionallows current to flow in both directions.

[0037] As shown in FIG. 3, the device 22-A is a remotely powerabledevice which includes a powerability indicator formed by a diode 70 anda resistor 72 connected in series between the centertaps 68 of thetransformers 64-A and 66-A. The powerability indicator provides, inresponse to a test signal, a response signal to the connecting medium 24indicating that the device 22-A is remotely powerable. In particular,the powerability indicator allows current to flow in only one direction(i.e., from the transformer 64-A to the transformer 66-A) which uniquelycharacterizes the device 22-A as a remotely powerable device. Incontrast, non-remotely powerable devices typically allow current flow inboth directions.

[0038] As further shown in FIG. 3, the power apparatus 26 connects tothe centertaps 68 of the transformers 64-B and 66-B of the device 22-Bthrough the connections 28. The power apparatus 26 provides the testsignal to the connecting medium 24 and receives the response signal fromthe connecting medium 24 through these connections 28 and the centertaps68 of these transformers 64-B and 66-B.

[0039] The connecting medium 24 includes multiple lines 76, 78. In onearrangement, the connecting medium 24 uses 802.3 based technology (e.g.,10BaseT, 100BaseT, etc.). In this arrangement, the connecting medium 24(e.g., Category 5 cabling) includes twisted pair wiring 76-1, 76-2(e.g., for carrying a differential signal pair between the device 22-Aand the device 22-B) and twisted pair wiring 78-1, 78-2 (e.g., forcarrying a differential signal pair between the device 22-B and thedevice 22-A). The connecting medium 24 connects to the devices 22through connectors 74 (e.g., RJ45 plugs and adaptors). When the remotelypowerable device 22-A is properly connected to the connecting medium 24,the powerability indicator of the remotely powerable device 22-A (thediode 70) allows current to flow only in one direction, from lines 76-1,76-2 to lines 78-1, 78-2.

[0040] The power apparatus 26, as shown in FIG. 3, includes controlcircuitry 80 and several direct current (DC) power supplies andswitches. In particular, the power apparatus 26 includes a −48 volt (V)DC power supply 82 which is controllable by a switch 84, a −5 VDC powersupply 86 which is controllable by a switch 88, and a +5 VDC powersupply 90 which is controllable by a switch 92. The control circuitry 80and switches 84, 88 and 92 form the controller 30 (see FIG. 1). Thepower supplies 82, 86 and 90 form the signal generator 32 (again, seeFIG. 1). The power apparatus 26 further includes current detectors 94-1and 94-2 which form the detector 34 (FIG. 1).

[0041] The control circuitry 80 is capable of selectively supplying −48volts, −5 volts and +5 volts to the connecting medium 24 by operatingthe switches 84, 88 and 92. In particular, when the control circuitry 80opens switches 84, 92 and closes the switch 88, the power supply 86provides −5 volts to the connecting medium 24 in order to measure acurrent response (the response signal). Similarly, when the controlcircuitry 80 opens switches 84, 88 and closes the switch 92, the powersupply 90 provides +5 volts to the connecting medium 24 in order tomeasure another current response. Additionally, when the controlcircuitry 80 opens switches 88, 92 and closes the switch 84, the powersupply 82 provides −48 volts to the connecting medium 24 in order toprovide phantom power to the device 22-A which connects to the remoteend of the connecting medium 24. It should be understood that thedevices 22-A and 22-B can communicate with each other through theconnecting medium 24 using differential pair signals while the powersupply 82 applies power to the device 22-A through the connecting medium24, i.e., while the device 22-A draws phantom power from the powerapparatus 26 through the connecting medium 24.

[0042] Furthermore, it should be understood that the power supplies 86,90 are preferably low current power supplies, i.e., capable of limitingthe current to less than an amp (e.g., 25-30 milliamps) in order toprevent damaging any non-remotely powerable devices connecting to theconnecting medium 24.

[0043] In one arrangement, the control circuitry 80 includes a dataprocessing device or processor. Here, a computer program product 98(e.g., one or more CDROMs, tapes, diskettes, etc.) provides instructionswhich direct the operation of the processor. Alternatively, theprocessor acquires the instructions through other means, e.g., via anetwork download through the device 22-B, or has non-volatile storageassociated with the processor (e.g., ROM, flash memory, etc.). Furtherdetails of the operation of the remote power system 20 will now beprovided with reference to FIGS. 4 and 5.

[0044]FIG. 4 shows a procedure 100 which is suitable for use as step 42of the procedure 40 (FIG. 2) performed by the power apparatus 26. Theprocedure 100 involves providing a test signal (e.g., multiple voltages)to the connecting medium 24 and measuring a response signal (e.g.,current).

[0045] In step 102, the power apparatus 26 begins supplying, to theconnecting medium 24, a first voltage during a first time period. Inparticular, the control circuitry 80 closes the switch 88 for 100milliseconds such that the −5 VDC power supply 86 applies −5 voltsacross the centertaps 68 of the transformers 64-B and 66-B. As a result,−5 volts appears across the diode 70 of the device 22-A which reversebiases the diode 70.

[0046] In step 104 and during the first time period, the power apparatus26 measures current through the connecting medium 24. In particular, thecontrol circuitry 80 activates the current detector 94-2 to determinewhether current flows through the connecting medium 24. Since the diode70 is reversed biased, no current flows through the connecting medium24, and the control circuitry 80 detects no current flow. FIG. 5 shows acircuit diagram having circuit elements which are suitable for use forthe current detector 94-2.

[0047] In one arrangement, the procedure 100 does not include step 106and step 104 proceeds to step 108. However, in another arrangement, theprocedure 100 includes step 106 which allows the power apparatus 26 toterminate the procedure 100 if it determines that there is no remotelypowerable device properly connecting to the connecting medium 24. Inparticular, in step 106, the power apparatus 26 determines whether theresponse signal indicates that a properly connected remotely powerabledevice possibly exists on the connecting medium 24. If so, step 106proceeds to step 108. If not, the procedure 100 terminates.

[0048] In step 108, the power apparatus 26 begins supplying, to theconnecting medium 24, a second voltage during a second time period. Inparticular, the control circuitry 80 of the power apparatus 26 closesthe switch 92 for 100 milliseconds such that the +5 VDC power supply 90applies +5 volts across the centertaps 68 of the transformers 64-B and66-B. As a result, +5 volts appears across the diode 70 of the device22-A which forward biases the diode 70.

[0049] In step 110 and during the second time period, the powerapparatus 26 measures current through the connecting medium 24. Inparticular, the control circuitry 80 activates the current detector 94-1to determine whether current flows through the connecting medium 24.Since the diode 70 is forward biased, current flows through theconnecting medium 24, and the control circuitry 80 detects this currentflow. The circuit diagram of FIG. 5 includes circuit elements which aresuitable for use for the current detector 94-1.

[0050] After step 110, the procedure 100 terminates. The results of theprocedure 100 can be used by the control circuitry 80 to determinewhether to provide power to the connecting medium 24. For example, thecharacteristic of allowing current to flow in only one direction fromlines 76 to lines 78 (FIG. 3) indicates that the device 22-A is aremotely powerable device. Accordingly, during steps 46 and 48 of FIG.2, the power apparatus 26 provides phantom power to the remotelypowerable device 22-A through the connecting medium 24.

[0051] As stated above, FIG. 5 shows a circuit diagram which includescircuitry which is suitable for use for each of the current detectors94-1 and 94-2. The current detector 94 includes a resistor 124 and acomparator 126 having its inputs connected to the ends of the resistor124. Accordingly, as current flows through the connecting medium 24 andthrough the resistor 124, the potential difference across the resistor124 is applied to the inputs of the comparator 126. The comparator 126provides an indication signal 128 indicating whether the potentialdifference exceeds a predetermined voltage threshold, i.e., whetherthere is current flow through the connecting medium 24.

[0052] It should be understood that one skilled in the art can select asuitable value for the resistor 124 (e.g., 10 ohms) in order to properlygenerate the indication signal 128. For example, suppose that eachtransformer 64, 66 provides approximately 20 ohms of resistance so thateach half coil provides 10 ohms of resistance. Further suppose that theconnecting medium is 26 gauge medium hardness wire having a resistanceof 42.4 ohms per foot and that the maximum length of the connectingmedium 24 is 100 meters (approx. 328 feet) thus translating into amaximum resistance per wire of 13.9 ohms. The resulting resistance fromthe power apparatus 26, through the transformer 64-B (5 ohms), throughthe wires 76 (6.95 ohms), through the transformer 64-A (5 ohms), throughthe diode 70 (31 ohms if the current is limited to about 25 milliamps),through the resistor 72 (100 ohms), through the transformer 66-A (5ohms), through the wires 78 (6.95 ohms), through the transformer 66-B (5ohms), and through the resistor 124 (10 ohms) is 174.9 ohms. If theapplied voltage is −5 volts, the current flow is approximately 28.6milliamps (−5 volts divided by 174.9 ohms). Accordingly, the voltagedrop across the sensing resistor 124 approximately 286 millivolts (10ohms times 28.6 milliamps) which is a value that is easily detectable bythe comparator 126 in order to properly provide the indication signal128.

[0053] Additionally, it should be understood that the power apparatus 26is capable of discovering other powerability conditions of the system 20of FIG. 1, i.e., of the computer network. In particular, the powerapparatus 26 can determine (i) when there is no device connecting to theconnecting medium 24 at the remote end, (ii) when there is areverse-wired remotely powerable device connecting to the connectingmedium 24 at the remote end, and (iii) when there is a shorted conditionor non-remotely powerable device connected to the connecting medium 24at the remote end. As stated above, when there is no device at theremote end of the connecting medium 24, there is no possible currentflow through the connecting medium 24 in either direction. When there isa reverse-wired remotely powerable device at the remote end of theconnecting medium 24, there is current flow when only in one directionwhich is opposite to the direction of current flow for a properlyconnected remotely powerable device. When there is a short in theconnecting medium 24 or a non-remotely powerable device at the remoteend, current is capable of flowing in both directions. Further detailsof how the power apparatus 26 makes such determinations will now beprovided with reference to FIGS. 6A, 6B and 6C.

[0054]FIG. 6A shows an arrangement 130 in which there is no device atthe remote end of the connecting medium 24, and in which an opencondition 132 exists at the remote end of the connecting medium 24.Accordingly, current cannot flow in either direction through theconnecting medium 24.

[0055] For the arrangement 130, the power apparatus 26 performs theprocedure 40 (FIG. 2). In step 42 of the procedure 42, the powerapparatus 26 provides a test signal to the connecting medium 24, andmeasures a response signal. In particular, the power apparatus 26performs the procedure 100 for step 42 (FIG. 4). That is, the powerapparatus 26 supplies −5 volts to the connecting medium 24 (step 102).Since no current flows through the connecting medium 24 due to the opencondition 132 at the remote end, the power apparatus 26 measures nocurrent flow (step 104).

[0056] Recall that if the remotely powerable device 22-A were properlyconnected to the remote end of the connecting medium 24 (FIG. 3), thepower apparatus 26 would also detect no current flow due to the reversebiasing of the diode 70 of the device 22-A. Since the power apparatus 26cannot yet distinguish between the open condition 132 and a presence ofa remotely powerable device 22-A, the power apparatus 26 does not yetconclude that the open condition 132 exists at the remote end.

[0057] The power apparatus then supplies +5 volts to the connectingmedium 24 (step 108 of FIG. 4). Again, the power apparatus 26 measuresno current flow (step 110), since no current flows through theconnecting medium 24 due to the open condition 132 at the remote end. Ifa remotely powerable device 22-A had been connected to the connectingmedium 24 at the remote end, current would have flowed through theconnecting medium 24 and the device 22-A. Since the power apparatus 26detects no current flow in either direction, the power apparatus 26concludes that there is the open condition 132 at the remote end of theconnecting medium 24 and does not supply an operating voltage (e.g., −48volts) to the connecting medium 24.

[0058]FIG. 6B shows an arrangement 140 in which there is abackwards-wired, or reverse-wired, remotely powerable device 22-A at theremote end of the connecting medium 24. Accordingly, current can flowonly in one direction which is opposite to the direction of current flowfor a properly connected remotely powerable device.

[0059] For the arrangement 140, the power apparatus 26 performs theprocedure 100 to provide a test signal to the connecting medium 24 andmeasure a response signal (also see step 42 of FIG. 2). That is, thepower apparatus 26 supplies −5 volts to the connecting medium 24 (step102 of FIG. 4) which forward biases the diode 70 of the reverse-wiredremotely powerable device 22-A. Accordingly, current flows through theconnecting medium 24, and the power apparatus 26 measures this currentflow (step 104). The presence of (i) a short in the connecting medium24, (ii) a reverse-wired remotely-powerable device 22-A at the remoteend, or (iii) a non-remotely powerable device at the remote end couldcause current to flow through the connecting medium 24 during thisphase.

[0060] In contrast, if the remotely powerable device 22-A were properlyconnected to the remote end of the connecting medium 24 (FIG. 3), thepower apparatus 26 would detect no current flow due to the reversebiasing of the diode 70 of the device 22-A. Accordingly, the powerapparatus 26 concludes that there is not a properly connected remotelypowerable device at the remote end of the connecting medium 24. In onearrangement, the power apparatus 26 terminates the procedure 100 at thispoint (step 106). In another arrangement, the power apparatus 26continues the procedure 100.

[0061] If the power apparatus 26 continues the procedure 100, the powerapparatus 26 supplies +5 volts to the connecting medium 24 (step 108)which reverse biases the diode 70 of the reverse-wired remotelypowerable device 22-A. Accordingly, the power apparatus 26 measures nocurrent flow through the connecting medium 24 (step 110). A short in theconnecting medium 24 or the presence of a non-remotely powerable devicewould have resulted in current flow in the connecting medium 24 duringthis phase. Since the power apparatus 26 detects current flow only inone direction which is opposite to the direction of current flow for aproperly connected remotely powerable device, the power apparatus 26concludes that a reverse-wired remotely powerable device 22-A exists atthe remote end of the connecting medium 24.

[0062]FIG. 6C shows an arrangement 150 in which there is a non-remotelypowerable device 152 at the remote end of the connecting medium 24 (oralternatively a short in the connecting medium 24). The non-remotelypowerable device 152 is a conventional device having its own powersupply and can be characterized as including transformers 154-A, 156-A,series-connected resistances 158, 160 (e.g., 75 ohms each) betweencentertaps of the transformers 154-A, 156-A, and a capacitance 162interconnected between ground 164 and an intermediate node of theseries-connected resistances 158, 160. The series-connected resistancesallow current to flow in both directions through the connecting medium24.

[0063] For the arrangement 150, the power apparatus 26 performs theprocedure 100 to provide a test signal to the connecting medium 24 andmeasure a response signal (also see step 42 of FIG. 2). In particular,the power apparatus 26 attempts to supply −5 volts to the connectingmedium 24 (step 102 of FIG. 4). In response, current flows through theconnecting medium 24 and through the series-connected resistances 158,160, and the power apparatus 26 measures this current flow (step 104).

[0064] If the remotely powerable device 22-A were properly connected tothe remote end of the connecting medium 24 (FIG. 3), the power apparatus26 would detect no current flow due to the reverse biasing of the diode70 of the device 22-A. Accordingly, the power apparatus 26 concludesthat there cannot be a properly connected remotely powerable device atthe remote end of the connecting medium 24. The cause of the currentflow could be (i) a short in the connecting medium 24, (ii) the presenceof a reverse-wired remotely powerable device at the remote end of theconnecting medium 24, or (iii) the presence of a non-remotely powerabledevice at the remote end of the connecting medium 24. In onearrangement, the power apparatus 26 terminates the procedure 100 at thispoint (step 106). In another arrangement, the power apparatus 26continues the procedure 100.

[0065] If the power apparatus 26 continues the procedure 100, the powerapparatus 26 supplies +5 volts to the connecting medium 24 (step 108)which, again, results in current flow through the connecting medium 24and the series connected resistances 158, 160. Accordingly, the powerapparatus 26 measures current flow through the connecting medium 24(step 110). The presence of a reverse-wired remotely powerable device atthe remote end of the connecting medium would have resulted in nocurrent flow during this phase. Since the power apparatus 26 detectscurrent flow in both directions, the power apparatus 26 concludes thatthere exists either a non-remotely powerable device connected to theconnecting medium 24 at the remote end, as shown in FIG. 6C, or thatthere is a shorted condition in the connecting medium 24.

[0066] As described above, the power apparatus 26 is capable ofdiscovering a variety of powerability conditions of the computernetwork, i.e., of the system 20. In one arrangement, the power apparatus26 includes an output device (e.g., an LED display) that indicates thedetection of particular powerability conditions (i.e., the conditions ofFIGS. 6A, 6B and 6C) of the computer network. Further details of theinvention will now be provided with reference to FIG. 7 which shows animplementation of the invention in a particular network topology (e.g.,a hub-and-spoke configuration).

[0067]FIG. 7 shows a computer network 170 having a data communicationsdevice 172 (e.g., an IP switch) and associated power apparatus 174 whichconnect with multiple devices 176-1, . . . , 176-N (collectively,devices 176) through connecting media 178-1, . . . , 178-N(collectively, connecting media 178). The power apparatus 174 performsthe procedure 40 for each connecting medium 178 to determine whether toprovide power to that connecting medium 178 (e.g., in a round robin orother multiplexed manner). If the power apparatus 174 discovers that aremotely powerable device connects to a remote end of a particularconnecting medium 178, the power apparatus 174 provides power remotelyto that device 178 (phantom power). Otherwise, the power apparatus 174does not provide remote power (to avoid damaging non-remotely powerabledevices) and waits a predetermined period of time (e.g., one to twominutes) and then rechecks that connecting medium 178 (see procedure 40in FIG. 2). For the devices 176 that are remotely powered by the powerapparatus 174 or have their own power sources (e.g., local powersources), the data communications device 172 communicates with thosedevices 176 over the respective connecting media 178. Accordingly, thecomputer network 170 enables data communications between devices andsafe application of remote power without risking damage to non-remotelypowerable devices.

[0068] As described above, the invention is directed to techniques fordiscovering a powerability condition of a computer network such as theexistence of a remotely powerable device attached to a connecting mediumof the computer network. Such detection can then determine whether aremote power source (e.g., a data communications device such as aswitch) provides remote power (e.g., phantom power) to the computernetwork. In particular, if it is determined that a remotely powerabledevice is attached to the computer network, the remote power source canprovide power to the device remotely (e.g., through the connectingmedium). However, if no remotely powerable device is discovered, theremote power source can avoid providing power remotely and thus avoidpossibly damaging any non-remotely powerable device on the computernetwork.

[0069] The invention leverages off of asymmetrical behavior of a remotedevice. If the application of stimuli to a computer network, whichpossibly has a remote device connected thereto, results in expectedbehavior, power can be safely applied to the remote device. However, ifthe behavior is not as expected, power can be withheld and theunexpected behavior can be identified. The features of the invention maybe particularly useful in computerized devices manufactured by CiscoSystems, Inc. of San Jose, Calif.

[0070] While this invention has been particularly shown and describedwith references to preferred embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the spirit and scope of theinvention as defined by the appended claims.

[0071] For example, step 48 of the procedure 40 of FIG. 2 describes thepower apparatus 26 as providing power indefinitely to a remotelypowerable device through the connecting medium 24. As an alternative,the power apparatus 26 can intermittently confirm that the remotelypowerable device is still connected to the remote end of the connectingmedium 24. This alternative minimizes possible damage if the remotelypowerable device is replaced with a non-remotely powerable device.

[0072] Additionally, it should be understood that the devices 22-A, 152and 176 can be a variety of communications devices such as IP phones,security/surveillance devices, etc. which are capable of drawing powerremotely. A powerability indicator (e.g., the diode 70 and the resistor72 series connected between centertaps 68 of the transformers 64-A,66-A) within each remotely powerable device provides an indication backto a remote power source (e.g., the power apparatus 26) that the deviceis remotely powerable.

[0073] Moreover, it should be understood that the devices 22-B, 172 canbe a variety of communications devices as well such as Voice over IP(VoIP) switches, IP switches, hubs, routers, bridges, etc. The devices22-B, 172 can form a single device with the power apparatus 26, 174 orreside separately from the power apparatus 26, 174. In one arrangement,the device 22-B, 172 is older equipment, and the power apparatus 26, 174connects the older equipment as an ancillary box.

[0074] Furthermore, it should be understood that FIG. 4 shows the powerapparatus 26 applying −5 volts to the connecting medium 24 (step 102)and then applying +5 volts to the connecting medium 24 (step 108), byway of example only. In another arrangement, the power apparatus 26applies +5 volts to the connecting medium 24 before applying −5 volts.In either arrangement, the power apparatus 26 indicates that a remotelypowerable device connects to the remote end of the connecting medium 24when the application of the +5 volts results in current flow, and theapplication of −5 volts results in no current flow (as measured in steps104 and 110). Of course, the system 20 can be reconfigured to indicatethat a remotely powerable device connects to the remote end of theconnecting medium 24 when the application of the −5 volts results incurrent flow, and the application of +5 volts results in no currentflow. Such modifications are intended to be within the scope of theinvention.

[0075] Additionally, it should be understood that the invention issuitable for use in network topologies other than the hub-and spokeconfiguration of FIG. 7. For example, the invention can be implementedin ring configurations that use point-to-point connections andterminations between devices, and other configurations.

[0076] Furthermore, it should be understood that the power apparatus 26can be configured to apply power to a remote device upon detection of areverse-wired remotely powerable device. For example, upon detection ofthe reverse-wired remotely powerable device 22-A of FIG. 6B, the powerapparatus 26 can be configured to provide power in a manner that enablesthe reverse-wired remotely powerable device 22-A to nevertheless operateproperly.

What is claimed is:
 1. A method for discovering a powerability conditionof a computer network, the method comprising the steps of: providing atest signal to a connecting medium of the computer network; measuring aresponse signal from the connecting medium of the computer network; andindicating whether a remotely powerable device connects to theconnecting medium of the computer network based on the response signal.2. The method of claim 1 wherein the computer network supportsconnection of a remotely powerable device that receives, during normaloperation, an operating voltage having a first voltage magnitude; andwherein the step of providing the test signal includes the step of:supplying, as the test signal, a test voltage having a second voltagemagnitude that is substantially less than the first voltage magnitude.3. The method of claim 1 wherein the step of providing the test signalincludes the step of: supplying, to the connecting medium, a firstvoltage during a first time period; and supplying, to the connectingmedium, a second voltage that is substantially different than the firstvoltage during a second time period.
 4. The method of claim 3 whereinthe step of supplying the first voltage includes the step of applyingone of a positive and negative test voltage to the connecting medium,and wherein the step of supplying the second voltage includes the stepof applying the other of the positive and negative test voltage to theconnecting medium.
 5. The method of claim I wherein the connectingmedium includes (i) a first connecting link having a local end thatterminates at a first transformer and a remote end, and (ii) a secondconnecting link having a local end that terminates at a secondtransformer and a remote end; and wherein the step of providing the testsignal includes the step of: applying the test signal to the connectingmedium through a centertap of the first transformer and a centertap ofthe second transformer.
 6. The method of claim I wherein the connectingmedium includes a local end and a remote end, and wherein the step ofindicating includes the step of: selectively identifying, through thelocal end of the connecting medium, one of (i) a backwards wired devicecondition at the remote end, (ii) an open condition at the remote end,(iii) a remotely powerable device condition at the remote end, and (iv)a shorted/non-powerable device condition at the remote end.
 7. Anapparatus for discovering a powerability condition of a computernetwork, comprising: a controller; a signal generator coupled to thecontroller; and a detector coupled to the controller, the controller (i)configuring the signal generator to provide a test signal to aconnecting medium of the computer network, (ii) configuring the detectorto measure a response signal from the connecting medium of the computernetwork, and (iii) indicating whether a remotely powerable deviceconnects to the connecting medium of the computer network based on theresponse signal.
 8. The apparatus of claim 7 wherein the computernetwork supports connection of a remotely powerable device thatreceives, during normal operation, an operating voltage having a firstvoltage magnitude; and wherein the controller configures the signalgenerator to supply, as the test signal, a test voltage having a secondvoltage magnitude that is substantially less than the first voltagemagnitude.
 9. The apparatus of claim 7 wherein the controller configuresthe signal generator to supply, to the connecting medium, (i) a firstvoltage during a first time period, and (ii) a second voltage that issubstantially different than the first voltage during a second timeperiod.
 10. The apparatus of claim 9 wherein the controller configuresthe signal generator to apply one of a positive and negative testvoltage to the connecting medium as the first voltage, and the other ofthe positive and negative test voltage to the connecting medium as thesecond voltage.
 11. The apparatus of claim 7 wherein the connectingmedium includes (i) a first connecting link having a local end thatterminates at a first transformer and a remote end, and (ii) a secondconnecting link having a local end that terminates at a secondtransformer and a remote end; and wherein the controller configures thesignal generator to apply the test signal to the connecting mediumthrough a centertap of the first transformer and a centertap of thesecond transformer.
 12. The apparatus of claim 7 wherein the connectingmedium includes a local end and a remote end, and wherein the controllerselectively identifies, through the local end of the connecting medium,one of (i) a backwards wired device condition at the remote end, (ii) anopen condition at the remote end, (iii) a remotely powerable devicecondition at the remote end, and (iv) a shorted/non-powerable devicecondition at the remote end.
 13. A remotely powerable device,comprising: normal operating circuitry that couples to a connectingmedium of a computer network; and a powerability indicator, coupled tothe normal operating circuitry, that (i) receives a test signal from theconnecting medium of the computer network, and (ii) provides a responsesignal to the connecting medium of the computer network to enablediscovery of the remotely powerable device based on the response signal.14. The remotely powerable device of claim 13 wherein the normaloperating circuitry is configured to receive, during normal operation,an operating voltage having a first voltage magnitude; and wherein thepowerability indicator is configured to provide the response signal inresponse to receipt of a test voltage, as the test signal, the testvoltage having a second voltage magnitude that is substantially lessthan the first voltage magnitude.
 15. The remotely powerable device ofclaim 13 wherein the powerability indicator is configured to provide theresponse signal in response to (i) a first voltage during a first timeperiod, and (ii) a second voltage that is substantially different thanthe first voltage during a second time period.
 16. The remotelypowerable device of claim 15 wherein the powerability indicator isconfigured to provide the response signal in response to (i) one of apositive and negative test voltage from the connecting medium as thefirst voltage, and (ii), the other of the positive and negative testvoltage from the connecting medium as the second voltage.
 17. Theremotely powerable device of claim 13 wherein the normal operatingcircuitry includes a first transformer and a second transformer; whereinthe connecting medium includes (i) a first connecting link having alocal end that terminates at the first transformer and a remote end, and(ii) a second connecting link having a local end that terminates at thesecond transformer and a remote end; wherein each transformer includes acentertap; and wherein the powerability indicator receives the testsignal through the centertap of the first transformer and the centertapof the second transformer.
 18. The remotely powerable device of claim 13wherein the connecting medium includes a local end and a remote end, andwherein the powerability indicator selectively indicates, through thelocal end of the connecting medium, one of (i) a backwards wired devicecondition at the local end and (ii) a remotely powerable devicecondition at the local end.
 19. An apparatus, comprising: normaloperating circuitry that communicates with a remote device over acomputer network during normal operation; and power circuitry, coupledto the normal operating circuitry, that discovers whether the remotedevice is remotely powerable over the computer network, the powercircuitry including: a controller; a signal generator coupled to thecontroller; and a detector coupled to the controller, the controller (i)configuring the signal generator to provide a test signal to aconnecting medium of the computer network, (ii) configuring the detectorto measure a response signal from the connecting medium of the computernetwork, and (iii) indicating whether the remote device is remotelypowerable based on the response signal.
 20. The apparatus of claim 19wherein the controller of the power circuitry configures the signalgenerator to provide power to the remote device through the computernetwork when the controller indicates that the remote device is remotelypowerable based on the response signal.
 21. A computer program productthat includes a computer readable medium having instructions storedthereon for discovering a powerability condition of a computer network,such that the instructions, when carried out by a processor, cause theprocessor to perform the steps of: providing a test signal to aconnecting medium of the computer network; measuring a response signalfrom the connecting medium of the computer network; and identifyingwhether a remotely powerable device connects to the connecting medium ofthe computer network based on the response signal.
 22. An apparatus fordiscovering a powerability condition of a computer network, comprising:a signal generator; a detector; and control means for (i) configuringthe signal generator to provide a test signal to a connecting medium ofthe computer network, (ii) configuring the detector to measure aresponse signal from the connecting medium of the computer network, and(iii) indicating whether a remotely powerable device connects to theconnecting medium of the computer network based on the response signal.23. A method for discovering a powerability condition of a computernetwork, the method comprising the steps of: providing a test signal toa connecting medium of the computer network; measuring a response signalfrom the connecting medium of the computer network; and determiningwhether a backwards-wired remotely powerable device connects to theconnecting medium of the computer network based on the response signal,and when it is determined that a backwards-wired remotely powerabledevice connects to the connecting medium, applying power to thebackwards-wired remotely powerable device.